Research On Catalytic Hydrogenation Performances Of Aluminium Oxide And MXene?Ti₃C₂? Supported Pd Catalyst

As the depletion of fossil fuels has become an increasingly prominent problem,searching efficient and environmentally friendly resources to replace non-renewable energy is seen as an imminent task.Researchers paid much attention to biomass energy for the features of the widespread and renewable.Catalytic hydrogenation of biomass to produce liquid fuels and fine chemicals is potentially important in the fields of renewable energy.Lignin is one kinds of biomass and can be directly converted into desired products to replace the existing chemicals related crude oils.The model molecules of lignin compounds were mainly studied for the catalytic hydrogenation of lignin due to the molecular structure of lignin is complex.Phenol and vanillin were widely studied because of their representative chemical structure.However,designing highly efficient,environmentally friendly,new catalysts and low-cost catalytic system for the selective hydrogenation of phenols and derivative phenolic molecules still remain challenges.In this work,we are focusing on supporting Pd nanoparticles on alumina oxide and 2D MXene?Ti₃C₂?materials for the catalytic hydrogenation of phenol and vanillin to produce cyclohexanone and 2-methoxy-4-methylphenol,respectively.The research contents and results were listed as follows:?1?Selective hydrogenation of phenol to cyclohexanone is an important process in both chemical industry and renewable feedstock processing.Here,we report that 99%conversion and 99%selectivity can be achieved over as-prepared Pd/?-Al₂O₃ catalyst under the medium of low-pressure CO₂?0.05-0.2 MPa?and H₂O at 373 K.In addition,the catalyst was used of five times without losing its activity and product selectivity in low-pressure CO₂.Ab initio calculations and in situ high-pressure FTIR measurements indicated enhanced selectivity of cyclohexanone in low-pressure CO₂ is originated from the molecular interaction between cyclohexanone and CO₂,which can prevent the further hydrogenation of cyclohexanone to cyclohexanol.Notably,enhancement of selectivity to cyclohexanone in low-pressure CO₂ was also achieved by using commercial Pd/?-Al₂O₃ and Pd/C catalysts.?2?MXene is a new family of 2D materials and has been widely applied in the fields of electrochemistry and energy storage because of its unique layer structure,excellent conductivity and chemical stability.However,MXene supported metal nanoparticles for heterogeneous catalysis has rarely been reported yet.MXene?Ti₃C₂?was produced by HF etching Ti₃AlC₂,and then the Pd/Ti₃C₂-NaOH and Pd/Ti₃C₂-HM catalysts were prepared by pretreatment of Ti₃C₂ with NaOH solution and N₂H₄·H₂O before supporting Pd nanoparticles.The Pd/Ti₃C₂-NaOH catalyst exhibited excellent catalytic activity for the hydrogenation reaction of vanillin?vanillin conversion and selectivity of 2-methoxy-4-methylphenol were all above 99%?.XPS and FTIR data show that the hydroxyl content of Ti₃C₂ changes significantly after pretreating with NaOH solution and N₂H₄·H₂O,which tuning the Pd particle size,metal dispersity and content of Pd⁰ of the catalysts.These properties of Pd/Ti₃C₂ catalysts has an important influence on the hydrogenation of vanillin.This work provides a reference for investigating the use of MXene?Ti₃C₂?as support to prepare metal nanoparticles in 2D layered structure for the application of catalytic hydrogenation.